Over the past five years, President Barack Obama has gained a reputation as a reluctant commander-in-chief. True, he has not shied away from endorsing drone strikes or the killing of Osama bin Laden. But on many questions – such as whether to take military action against the Syrian regime after its use of chemical weapons – he has often appeared indecisive.

This week, however, the president responded firmly and speedily to events in the East China Sea. Last Saturday China announced it was setting up an “air defence identification zone” around a group of islands that Japan administers but which China claims.On Tuesday the US promptly responded by sending two B-52 bombers into the contested area without notifying the Chinese authorities. The US message was clear: America will resist any attempt to change the status quo over the islands by force.

Nobody doubts that a conflict involving China, Japan and the US over these uninhabited rocks would be disastrous. The stand-off is certainly alarming. On Friday China scrambled combat jets as Japanese fighter aircraft entered the air defence zone. There is a growing sense of a storm gathering over the western Pacific.